Various systems for connecting components of a prosthesis together have been proposed.
See, for example, Richter, H. G., Willmann, G., Wimmer, M., and Osthues, F. G., “Influence of the Ball/Stem-Interface on the Load Bearing Capability of Modular Total Hip Endoprosthesis,” Modularity of Orthopedic Implants, ASTM STP 1301, Donald E. Marlowe, Jack E. Parr, and Michael B. Mayor, Eds., American Society for Testing and materials, 1997 (hereinafter “Richter et al.”).
More particularly, Richter et al. discusses a study in which “the surface structure of metal tapers is varied systematically in order to evaluate the influence of groove depth and pitch on the resistance to static load.”
Additional examples of systems for connecting components of a prosthesis together include the systems described in the following U.S. patents:
U.S. Pat. No. 4,225,981 issued Oct. 7, 1980 to Zeibig relates to an endoprosthesis with a metal-ceramic union. More particularly, this patent relates to a bone joint endoprosthesis in which the spigot of the metal shank is externally threaded to mate with a thread inside the ceramic head of the prosthesis; the thread on the spigot has greater depth in the radial direction, with flat sides, and the depth of the thread in the head is more shallow.
U.S. Pat. No. 5,584,629 issued Dec. 17, 1996 to Bailey et al. relates to a connector for medical implant. More particularly, this patent relates to a connection for components in a medical implant assembly which utilizes a tapered mating surface on each component with cylindrical splines and flutes formed on each mating surface such that the surfaces are complementary to the extent that the splines of one surface are received in the flutes of the adjacent surface. The patent indicates that each surface is continuous with no discontinuity which would act as a stress raiser or enhance concentration of stress in one locale. The complementary surfaces are urged into registry by a screw connection coaxially through the surfaces.
U.S. Pat. No. 5,865,850 issued Feb. 2, 1999 to Matthews relates to a coated load bearing surface for a prosthetic joint. More particularly, this patent relates to a prosthetic hip joint including a ceramic hip head having a bore which defines a surface, wherein the bore surface has a layer of malleable material disposed on at least a portion thereof. The surface of the bore includes surface imperfections in the form of peaks and valleys. The prosthetic hip joint can also include a femoral component having a trunnion with a tapered surface adapted for friction fit insertion into the bore of the hip head. The patent indicates that the layer of material, such as pure titanium, distributes a load on the joint reducing localized stress points produced by opposing asperity peaks in the load-bearing surfaces of the bore and trunnion.
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof.